Magnetohydrodynamic pump



June 2, 1964 o. M. STUETZER MAGNETOHYDRODYNAMIC PUMP 2 Sheets-Sheet 1Filed April 30, 1962 FIG. 2

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OTMAR M. STUE ZER 22/ ATTORNEY June 2, 1964 O. M. STUETZERMAGNETOHYDRODYNAMIC PUMP Filed April 30, 1962 2 Sheets-Sheet 2 s W v HQ11-9w 1 as 51%53'Efl/ INVENTOR.

OTMAR M. STUETZER ATTORNEY United States Patent O 3,135,208MAGNETOI-IYDRODYNAMIC PUMP Otmar M. Stuetzer, Hopkins, Minn., assignor,by mesne assignments, to Litton Systems, Inc., Beverly Hills, Calif., acorporation of Maryland Filed Apr. 30, 1962, Ser. No. 191,235 4 Claims.(Cl. 1031) This invention relates to pumps, and, more particular.- ly,to an improved pump for pumping conductive fluids, which operates on theprinciples of magnetohydrodynamics.

Magnetohydrodynamics is that field of science which deals with thereactions induced in an electrically conductive fluid in the presence ofa magnetic field. It is, in effect, a union of two branches of physicalscience, one dealing with fluid flow and the other with electromagneticfields. For a theoretical treatment of the phenomena ofmagnetohydrodynamics, reference may be made to a book entitledMagnetohydrodynamics by R. K. M. Landshoff, Stanford University Press,1957, and to a book entitled Magnetohydrodynamics by T. G. Cowling,Interscience Publishers, Inc., New York, New York, 1957. In addition,many scientific and technical papers have been published on the subjectWithin the last several years.

It is known that if a highly conductive fluid is placed in a magneticfield and current is passed through the fluid at right angles to themagnetic field, the fluid is pumped in a direction normal to both themagnetic field and the direction of current flow. This phenomenon hasbeen investigated for many years and various pumps operating on thismagnetohydrodynamic principle have been proposed. Each of the pumpsheretofore known has, by necessity, included means to provide a magneticfield extending across and normal to the flow path of the conductivefluid. In the case of a direct current pump, a permanent magnet could beused to provide the magnetic field, but, in the case of an alternatingcurrent pump, means were required to reverse the magnetic field insynchronism with the reversals of the pumping current.

In either case, the magnetic field required was relatively high, whichnecessitated the use of correspondingly large magnets or inductioncoils. The magnetohydrodynamic pump of the present invention is believedto constitute a major improvement over such pumps heretofore known, inthat no external means are required to provide a magnetic field acrossthe flow path of the conductive fluid. In addition, the pump of thepresent invention is usable with pumping currents ranging in frequencyall the Way from direct current to microwave frequencies of alternatingcurrent.

In its broader aspects, the present invention provides amagnetohydrodynamic pump for pumping conductive fluids, which comprisesmeans defining a flow path for the fluid with two electrodes located inthe flow path. The first electrode has an aperture to permit fluid flowthrough the electrode, and it substantially completely obstructs theflow path except for the aperture. The second electrode is spacedupstream from the first electrode; it is solid and is so shaped as topermit fluid to flow between the two electrodes and through the aperturein the first electrode. Means are provided for energizing the electrodesto cause electrical current to flow through the conductive fluid betweenthe two electrodes.

It is well known that, when current flows through a conductor, amagnetic field is created about the conductor by the current flow. Inthe present case, the current flowing between the two electrodes of thepump creates a magnetic field in that area between the two electrodes,which is at right angles to the direction of current flow between theelectrodes. Thus, the fluid is pumped in a direction normal to both themagnetic field and the direc- 3,135,208 Patented June 2, 1964 lCe tionof current flow without the use of an external magnet or coil.

The invention, together with various objectives and advantages, will bebetter understood by reference to the following description of severalembodiments, taken in conjunction with the accompanying drawings, inwhich FIGS. 1, 2 and 3 are diagrammatic sectional views of threeembodiments of single-stage pumps constructed according to theinvention; and

FIG. 4 is a diagrammatic sectional view of another embodiment of theinvention utilizing two pumping stages.

FIG. 1 illustrates diagrammatically a relatively simple embodiment ofthe invention that may be conveniently used to illustrate its principlesof operation. The magnetohydrodynamic pump shown comprises a conduit 10having an upper section 1011 and a lower section 10b, which togetherdefine a flow path for the conductive fluid to be pumped. The conduit 10is made of an insulating material, such as glass or ceramic, and theupper section 10a is of smaller cross-sectional area than the lowersection 10b. The cross-sectional shape of the conduit 10 is of noparticular importance and it may conveniently be either cylindrical orrectangular. The upper and lower sections may be made integrally witheach other or they may be separate sections joined together byconventional means, such as the cement 11.

An electrode 12 is positioned within the smaller upper section 10a ofthe conduit and is provided with an aperture 12a, which extendssubstantially through the center of the electrode on the axis of theconduit. The crosssectional shape and size of theelectrode 12 is thesame as that of the upper conduit section 10a so that the electrodesubstantially completely obstructs the fiow path except for the aperture12a throughthe electrode.

A second electrode 13 is positioned in the larger section 10b of theconduit and spaced from the bottom surface of the first electrode 12.-The electrode 13 is of the same cross-sectional shape and size as theelectrode 12, and the facing surfaces of the two electrodes (that is,the lower surface of the electrode 12 and the upper surface of theelectrode 13) are substantially planar. The

electrode 13 is provided with a recess 13a in its upper surface intowhich an insulating plug 14 is set. The shape of the recess 13a issubstantially the same as that of the aperture 12a in the upperelectrode 12 and its depth is of no particular significance.

The two electrodes 12 and 13 are connected across a potential source 15.The potential source 15 is shown as being of the alternating currenttype but, as previously noted, the frequency of the voltage source mayvary over an extremely wide range from direct current up to microwavefrequencies of alternating current.

In operation, when the conduit 10 is filled with a conductive fluid andthe voltage source 15 is connected as shown, current flows between thetwo electrodes 12 and 13. This current, which is quite high because ofthe very low resistance of the conductive fluid, creates magnetic fluxwhich follows concentric circles about the axis of symmetry of the ductand the electrodes. This, together with the current density in theslots, causes a pressure P to be built up normal to both the magneticfield and the direction of current flow, that is, from the outside tothe inside of the electrodes. If the direction of current flow reversesalternating current), the magnetic field also reverses, so that thepressure does not reverse. The pressure P may be approximated by theexpression the diameter of the two electrodes. Thus, it is seen that thecurrent flowing between the electrodes has to hydrodynamic pump of theinvention may be of several types, and the invention is in no waylimited to the use of any particular fluid. Examples of suitable fluidsare the liquid forms of mercury, gallium and sodium, or a suitablehighly conductive electrolyte. In addition the invention contemplatesthe use of a highly conductive hot gas plasma as a conductive fluid. Theprincipal qualification is that the fluid to be pumped must be highlconductive. r

The embodiment of the invention shown diagrammatically in FIG. 2 is verysimilar to that shown in FIG. 1 and those parts in FIG. 2 bearing aprime superscript may be identical to the corresponding parts shown inFIG. 1. The principal difference between the two pumps is that theelectrode 12 in the embodiment shown in FIG. 1, which has asubstantially planar lower surface, is

I replaced by an electrode 18 having a differently shaped lower surface.The electrode 18 is provided with an 7 axial aperture 18a to permit thepassage of fluid, and i with a frusto-conical lower surface 18b. Thelower surface 18b of the electrode is so shaped that it is farthest fromthe upper planar surface of the electrode 13 at its outer edge. Thereason for the frusto-conical shape of the lower surface of theelectrode 18 is that it leads to a better distribution of the magneticfield existing across the space between the electrodes 18 and 13.therwise, the operation of the pump shown in FIG. 2 is identical withthat shown in and described with reference I to FIG. 1.

FIG. 3 illustrates diagrammatically an embodiment of the invention that,because of a somewhat modified electrode configuration, provides ahigher current density and consequent higher magnetic field between thecooperating surfaces of the two electrodes. .In that embodiment, theflow path for the conductive fluid is defined by an outer conduit 20 andby a concentrically arranged inner conduit 21, both conduits 20 and 21being made of an insulating material. Secure to the lower ends of theconduits 20 and 21 and coaxial with conduits is an electrode 22 having.a plurality of slots 22a extending through it in the area between theinner and outer conduit. A second electrode 23 is coaxially mountedbelow the first electrode 22 and may be spaced apart from it by aninsulating cylindrical spacer 24.

Pumping action is provided in the embodiment shown in FIG. 3 in thevolume betweenthe surface of an aperture 22b formed through'theelectrode 22 and the surface of a conical portion 23a formed on theelectrode 23. The aperture 22b in the electrode 22. and the conicalportion 23a on the electrode 23 are preferably coaxial with the axis ofthe inner-conduit 21. The aperture 22b is frustoconical in shape, beingwidest at its lower end adjacent the electrode 23, and the conicalportion 23a of the electrode 23 extends into the aperture. It isparticularly pointed out that the angle of the converging surface of thefrusto-conical aperture 22b is less acute than is the angle of theconverging surface of the conical portion 23a of the electrode 23.Because of this configuration, the magnetic field is well distributedthroughout the pumping space and the current density may be made quitehigh. In order to prevent current from flowing in other than the pumpingspace, a layer of insulating material 25 may cover those portions of theelectrode 23, other than the conical portion 23a, which are in contactwith the conductive fiuid.

When the electrodes 22 and 23 are connected across a voltage source 26,pumping occurs in the same manner as previously described. A highdensity current flows be tween the electrode 22 and the conical portion23a of the electrode 23, which creates a high magnetic field at rightangles to the direction of current flow. This results in pressure beingcreated which forces the conductive fluid to flow in a direction normalto both the magnetic field and the direction of current flow between theelectrodes, that is, upwardly through the space between the conicalportion 23a and the surface of the aperture 22b and out through theaperture 23b. Thus, the liquid flows downwardly through the outerconduit 2th, through the apertures 22a in the electrode 22, through theaperture 221), and then upwardly through the conduit 21.

FIG. 4 illustrates diagrammatically an embodiment of the inventionutilizing two pumping stages 33 and 31 arranged in series. Because thetwo stages 30 and 31 are identical in construction, only the pumpingstage 30 will be described in detail.

The flow path for the conductive fluid is defined by a conduit 32 madeof an insulating material. The upper pump stage 30 comprises anelectrode 33 having an axial frusto-conical aperture 33a. Arrangedupstream from the electrode 33 is a second electrode 34 having a conicalportion 34a which extends into the aperture 33a. The electrodes 33 and34 may be conveniently separated by insulating spacers 35. Again, as inthe embodiment shown in FIG. 3, the converging surface of thefrustoconical aperture 33a is less acute than is the angle of theconverging surface of the conical portion 34a, so that the two surfacesare spaced farther apart at the upstream end of the aperture 3311 thanat the downstream end. In order to prevent undesired current flowbetween nonpumping portions of the electrodes 33 and 34, a layer ofinsulating material 36 may be provided on the lower surface of theelectrode 33, and a similar layer 37 may be provided on the uppersurface of the electrode 34. Thus, current flow, and hence pumpingaction, are restricted to the space between the surface of the aperture33a and the conical portion 340.

When the electrodes 33 and 34 are connected across a voltage source 38,pumping action occurs which is very similar to that previously describedwith reference to the other embodiments of the invention. The highdensity current flowing between the surface of the aperture 33a and thesurface of the conical portion 34a causes a magnetic field to be set upat right angles to the direction of current flow. As a consequence, theconductive fluid which fills the conduit is pumped in a direction normalto both the direction of current flow and the direction of the magneticfield, and the fiuid is forced upwardly through the aperture 33a.

The lower pumping section 31, which is separated from the uper sectionby insulating spacers 39, operates in a fashion identical to that of theupper pumping section 30. As many pumping sections may be arranged inseries as are necessary to suit the pressure requirements of theparticular application involved.

In some applications, it may be desirable to connect the pump sections30 and 31 electrically in series rather than in parallel as shown. Thismay easily be done by replacing one or more of the insulating spacers 39with a conductive spacer. In that case, the collector electrode of theupper section and the emitter electrode of the lower section would beconnected to the two sides of the voltage source 38, and the other twoelectrodes would be electrically connected only to each other.

Although the various embodiments of the invention have been illustrateddiagrammatically with some constructional details omitted for the sakeof clarity, it is believed that the invention has been fully described.The

various details not described are all felt to be conventional and theirprovision well within the capabilities of one skilled in the art. Forexample, the various glassto-metal seals may be made by well knownmeans, and the electrodes may be conventionally mounted in the conduitson brackets or spiders.

It is now apparent that the invention provides a magnetohydrodynamicpump which possesses a number of advantages over those previously known.Of course, its outstanding advantage is that it requires no magneticfield that must be externally provided. It may be used with a voltagesource of virtually any frequency, because when the pumping currentbetween the two electrodes of the pump reverses in accordance with thealternations of the voltage source, the magnetic field caused by thecurrent also reverses. Therefore, pumping action always occurs in thesame direction. Each of the various embodiments of the invention issymmetrical in construction and, therefore, it is extremely simple andeasy to manufacture. In addition, very small voltages are involved, sothat there is little danger of injury to personnel using the pump.Although several embodiments of the invention have been described, it isapparent that many modifications and variations may be made by oneskilled in the art without departing from the spirit and scope of theinvention.

What is claimed is:

1. A magnetohydrodynamic pump for pumping conductive fluids comprisingmeans defining a flow path for said fluid, a first electrode in saidflow path and having an aperture to permit fluid flow through said firstelectrode, said first electrode substantially completely obstructingsaid flow path except for said aperture, a second electrode in said fiowpath spaced upstream from said first electrode, said second electrodebeing solid and shaped to permit said fluid to flow between said firstand second electrodes and through said aperture in said first electrode,said aperture being frusto-conical in shape and being widest adjacentsaid second electrode, and said second electrode including a conicalportion extending into said aperture, and means for causing electricalcurrent to flow through said conductive fluid between said first andsecond electrodes to provide a magnetic field in the space between saidelectrodes.

2. The magnetohydrodynamic pump defined by claim 1, wherein the angle ofthe converging surface of said frusto-conical aperture is less acutethan the angle of the converging surfaces of said conical portion ofsaid second electrodes.

3. A magnetohydrodynamic pump for pumping conductive fluids comprisingmeans defining a flow path for said fluid, a first electrode in saidflow path and having an aperture to permit fluid flow through said firstelectrode, said aperture being substantially in the center of said firstelectrode and being frusto-conical in shape and being widest adjacentsaid second electrode, said first electrode substantially completelyobstructing said flow path except for said aperture, a second electrodein said flow path spaced upstream from said first electrode, said secondelectrode being solid and shaped to permit said fiuid to flow betweensaid first and second electrodes and through said aperture in said firstelectrode, said first and second electrodes being axially aligned insaid flow path with said second electrode including a conical portionextending into said aperture, and means for causing electrical currentto flow through said conductive fluid between said first and secondelectrodes to provide a magnetic field in the space between saidelectrodes.

4. The magnetohydrodynamic pump defined by claim 3, wherein the angle ofthe converging surface of said frusto-conical aperture is less acutethan the angle of the converging surface of said conical portion of saidsecond electrode.

References Cited in the file of this patent UNITED STATES PATENTS902,106 Northrup Oct. 27, 1908 1,660,407 Bainbridge Feb. 28, 19282,669,183 Godbold Feb. 16, 1954 FOREIGN PATENTS 698,623 Great BritainOct. 21, 1953 718,429 Great Britain Nov. 17, 1954 OTHER REFERENCESTextbook of Physics, by Poynting and Thomson, pp. 138 and 139, 1920edition.

1. A MAGNETOHYDRODYNAMIC PUMP FOR PUMPING CONDUCTIVE FLUIDS COMPRISINGMEANS DEFINING A FLOW PATH FOR SAID FLUID, A FIRST ELECTRODE IN SAIDFLOW PATH AND HAVING AN APERTURE TO PERMIT FLUID FLOW THROUGH SAID FIRSTELECTRODE, SAID FIRST ELECTRODE SUBSTANTIALLY COMPLETELY OBSTRUCTINGSAID FLOW PATH EXCEPT FOR SAID APERTURE, A SECOND ELECTRODE IN SAID FLOWPATH SPACED UPSTREAM FROM SAID FIRST ELECTRODE, SAID SECOND ELECTRODEBEING SOLID AND SHAPED TO PERMIT SAID FLUID TO FLOW BETWEEN SAID FIRSTAND SECOND ELECTRODES AND THROUGH SAID APERTURE IN SAID FIRST ELECTRODE,SAID APERTURE BEING FRUSTO-CONICAL IN SHAPE AND BEING WIDEST ADJACENTSAID SECOND ELECTRODE, AND SAID SECOND ELECTRODE INCLUDING A CONICALPORTION EXTENDING INTO SAID APERTURE, AND MEANS FOR CAUSING ELECTRICALCURRENT TO FLOW THROUGH SAID CONDUCTIVE FLUID BETWEEN SAID FIRST ANDSECOND ELECTRODES TO PROVIDE A MAGNETIC FIELD IN THE SPACE BETWEEN SAIDELECTRODES.